On Tue, 2007-10-30 at 10:58 -0400, Paul Christensen wrote:
> > "Cuz an Omni VI doesn't have ALC jack. Where you going to pug it in?
> 73 de K1ESE
> John"
>
> There's nothing wrong with the concept of ALC between the transceiver and an
> amp, but more often than not, the real-world implementation is nothing more
> than a "feel good" exercise that leaves the operator with a false sense of
> security.
>
> >From what I've seen, the better ALC systems are employed within a product
> line under one manufacturer where the designer can calculate the ALC voltage
> "meet me" point with some semblance of precision. For this reason, ALC
> within the transmitter section of the transceiver is much easier to manage.
> Even when some form of ALC voltage adjustment is used between an amp and
> transceiver of different manufacturers, the ALC transient dynamics may not
> be optimized. Simply connecting an ALC cable between a transceiver and amp
> is no guarantee of good linearity and amp protection.
>
> For this reason, I have always shunned the use of ALC and try to pay
> attention to proper amp drive level and loading to ensure maximum linearity.
So you NEVER get excited and shout when chasing DX, so never drive the
PA to clipping??? If that never happens you are one cool ham.
> A better means of proper amp operations includes the use of a scope in
> trapezoid X-Y mode between the input and output of the amp.
But it may not always inspire you to keep from a bit of peak
compression, will it? A little bit of peak compression can show up as a
lot of higher order intermod, otherwise known as splatter.
>
> Until the advent of DSP, an even better method consisted of applying mic
> audio to one set of scope plates while applying final RF to the opposite
> set. The benefit is that the entire system from mic to amp antenna port is
> used to measure total system linearity. However, since transmit DSP
> introduces latency, even if slight, I've found that method no longer gives
> an accurate display of linearity.
It didn't work too good in the analog AM transmitter either because of
frequency
sensitive phase shifts through the audio chain. And for SSB the fundamental is
that the envelope of the SSB signal is not the same as the envelope of the
audio
from the microphone so it won't work at all for SSB.
>
> Paul, W9AC
>
73, Jerry, K0CQ
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|